Development of Simultaneous Removal System for Radioactively Gaseous and Particulate Matters generated by Dismantlement of Nuclear Power Plants

目前的工作旨在开发一种同时去除老化核电站拆除过程中由热切割活化钢结构产生的气体和颗粒物质的系统。本文以八羰基二钴（OCDC）为研究对象，对其气相行为进行了研究。OCDC是一种在钢结构热切削过程中具有高放射性的钴化合物。将正己烷制备的OCDC溶液雾化后，过滤成雾，生成OCDC蒸汽。然后，我们测量了它在不同停留时间下的分解速率，它的蒸汽浓度和温度，基于这个反应是通过中间体的连续一级反应的假设。结果发现，前一种分解为中间体的过程在这些反应中占主导地位。同时，考虑分解管作为扩散管调节反应停留时间，对生成的颗粒大小进行了估计，得到的颗粒大小估计至少大于1 nm。这些结果表明，我们需要形成的OCDC蒸汽停留时间大于20s，并且周围温度略高于室内温度，才能将其转化为颗粒并随后使用HEPA过滤器去除它们。

The present work is aimed at developing a simultaneous removal system for gaseous and particulate matters generated by thermal cutting of activated steel constructions during the dismantlement of aged nuclear power plants. In the present work, we focused on octacarbonyl di-cobalt(OCDC), which belongs to cobalt-compounds with high radioactivity during the thermal cutting of steel constructions, and investigated its behaviors in gas phase. OCDC vapor was generated by atomization of OCDC-solution prepared with hexane followed by filtration of the formed mists. Then, we measured its decomposition rates at various residence times, its vapor concentrations and temperatures based on the assumption that this reaction is consecutive first-order reactions via an intermediate. As a result, it was found that the former process of decomposition into the intermediate dominates these reactions. Also, we estimated the size of generated particles, considering the decomposition tube to adjust the residence time for reaction as a diffusion tube, and obtained that the size was estimated to be at least larger than 1 nm. These findings suggested that we need the residence time of formed OCDC vapor more than 20s and the surrounding temperature somewhat higher than room one in order to convert it into particles and subsequently remove them with HEPA filters.